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    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
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<body>
    <div>
        <span onclick="circle()">圆的面积</span>
        
    </div>
    <div class="toggle">
        <button type='button' onclick="circulation()">循环5次弹窗</button>
    </div>
    <div>
        <button type="button" onclick="click()" id="btn1">求点击</button>
    </div>
    <script>
        function circle(){
            var r=10;
            var result=parseFloat(3.14)*r*r;
            document.write(result);
        }
        function de_weight(){
            var str=["john","lily","lily","lucy"];
             list=[];
            for(var i=0;i<str.length;i++){
                if(!list.contains(str[i])){
                list.push(str[i]);
                }    
            }
        }
        function DayOfYear(d){
            var months= [31,28,31,30,31,30,31,31,30,31,30,31]
           
        }
        function circulation(){
            for(var i=0 ;i<5;i++){
                alert("弹出第"+(i+1)+"次窗口");
            }
        }
        function click(){
            document.getElementById("btn1").innerHTML='谢谢';
        }
    </script>
</body>
</html>